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Which Age Group—Old or Young—Should Get the COVID-19 Vaccine First May Depend on Timing

A young female medical professional holds a vaccine.

By Chris Bauch, University of Waterloo; Madhur Anand, University of Guelph, and Peter C. Jentsch, University of Waterloo

COVID-19 vaccines are on the horizon. Lately, it seems like each week brings news of another clinical trial demonstrating vaccine efficacy. But if supplies are initially limited, decision-makers will need to make hard choices about who should get them first.

One approach is to prioritize groups who are most vulnerable to serious outcomes like hospitalization and death, such as the elderly. Another approach is to prioritize groups who are most responsible for spreading the infection. The question is which approach will work best in a given population.

Our team decided to study this question using our combined 30 years of experience in population modelling, including the 2003-04 SARS outbreaks and the 2009 H1N1 pandemic. We developed a mathematical model of COVID-19 transmission and vaccination in Ontario, published as a preprint (a manuscript yet to be checked for errors). The types of models we employ are not mere mathematical abstractions or theories, but rather have been validated for many similar respiratory infections over the past three decades.

We found that if vaccination starts sufficiently early in 2021, a strategy of vaccinating individuals 60 years of age and older will prevent the most deaths. But more surprisingly, we found that if the vaccine is not available until later in 2021, we might be able to prevent more deaths by first vaccinating younger age groups — working-age adults and children — who have more contacts with others.

Vaccines can protect the unvaccinated

To understand this result, we must first explain that vaccines work in two ways. First, they provide direct protection: the vaccinated person doesn’t get infected. Second, they also provide indirect protection: the vaccinated person does not pass infection on to others. We do not yet know if the COVID-19 vaccines will prevent the passing of infection to others, but such transmission-blocking effects are a common feature of most licensed vaccines.

If enough people are vaccinated, the level of indirect protection in a population can be high. And indirect protection can be very powerful. Had it not been for indirect protection, smallpox would never have been globally eradicated in 1977. Once a sufficient number of individuals are vaccinated, herd immunity is achieved. But it is achieved through a kinder, gentler means than letting everyone become infected, and the virus is thereby eliminated from the population. Hence, indirect protection can have very strong effects in real populations.

Black and white photo of a young Black man
Ali Maow Maalin, of Merka, Somalia, had the world’s last recorded case of endemic smallpox in 1979. The WHO smallpox eradication campaign was launched in its intensified form in 1967, and in four years had wiped out smallpox in Latin America. Four more years toppled the disease’s last bastion in Asia. The multi-national teams closed in on Somalia, scene of ‘the last stand.’ The eradication of smallpox from the world was certified by the Global Commission, an independent panel of scientists drawn from 19 nations, in December 1979 at WHO Headquarters, in Geneva. (WHO/John F. Wickett)

This is not just the prediction of a mathematical model. This effect has been observed in empirical data on influenza vaccination from Japan, where vaccination of schoolchildren was found to reduce deaths in the elderly. Similarly, some jurisdictions practice cocooning, where if a vaccine does not work in a vulnerable person due to their advanced age or an immature immune system, we vaccinate the people around them instead. This approach is also recommended for the COVID-19 vaccines.

Conditions will change later in the pandemic

We think the switch in strategy between early and late 2021 predicted by our model occurs because indirect protection from vaccines will become stronger, later on in the pandemic.

In the early stages of a pandemic, most people are still susceptible. Therefore, if a few individuals are immune because of the vaccine, they don’t protect their contacts since there are too many other ways their contacts could get infected, as illustrated on the left side of the diagram.

However, as time goes on, more individuals will become infected and gain immunity. Under these conditions, adding more immune individuals to the population by vaccination can work more effectively to protect their contacts, as seen on the right side of the diagram. In other words, chains of transmission are replaced by chains of protection. At some point, more deaths can be prevented through indirect protection instead of direct protection.

Side-by-side diagrams of infection transmission
When there are many susceptible individuals (left), there are not enough individuals with immunity from previous infection to break up chains of transmission, so their immunity does not help others. But later on in the pandemic when there are fewer susceptible individuals (right), adding more immune individuals to the population through vaccination breaks chains of transmission more easily. Author provided

How to apply this approach

Our model was designed to provide insight into how vaccines work, and not to comment on specific policy recommendations. There are also important caveats to our study. For instance, we did not study a strategy of prioritizing residents of long-term care facilities, most of whom are older than 60 years of age. We also assumed that COVID-19 immunity is long-lasting, although evidence on this is still accumulating. However, the effect we identify relies upon well-validated principles of infectious disease epidemiology, and we found the effect persisted under the various scenarios explored by our modelling.

To apply these ideas in practice, public health authorities would first need to assess population immunity through a survey that tests population blood samples for COVID-19 antibodies a few months before vaccination starts. They could then plug these numbers into a mathematical model to determine whether they should prioritize the elderly, or instead prioritize groups that spread the infection the most.

We think this approach could be feasible. Standard mathematical modelling frameworks could be used, and their predictions are more reliable when predicting months ahead instead of an entire year. Also, antibody surveys are a more accurate way to determine a population’s infection history than case notifications, which would make the model predictions less subject to uncertainties.

Ethical dimensions, and looking to the future

Some might argue that the clear ethical choice is to give the vaccine first to those who are most vulnerable to fatality from the disease. We argue that decisions should be based on best available evidence and consider both direct and indirect effects. If the evidence suggests we can prevent more deaths in the elderly by vaccinating other age groups first, then that is the ethical decision. In other words, the right thing to do requires careful and sometimes nuanced thinking, but always evidence.

Indirect protection may seem like an abstract concept in the grip of a fast-moving pandemic. However, looking ahead , and with hope, we think it will be practically impossible to globally eradicate COVID-19 without it, just as in the case of smallpox. Vaccination policies will have to take advantage of indirect protection sooner or later, in one context or another.

Chris Bauch, Professor of Applied Mathematics, University of Waterloo; Madhur Anand, Professor & Director, Global Ecological Change & Sustainability Laboratory, University of Guelph, and Peter C. Jentsch, PhD Candidate, Applied Mathematics, University of Waterloo

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Coronavirus Travel Advisory Canada: Here’s What Canadians Should Know

Wuhan seafood market closed after the New Coronavirus was detected there for the first time. (Jan. 20, 2020.)
Wuhan seafood market closed after the New Coronavirus was detected there for the first time. (Jan. 20, 2020.)

Since the first case of novel coronavirus was reported in China in late December 2019, this new strain of virus has spread around the globe. To date, there have been more than 23,000 confirmed infections in more than 25 countries, and the death toll is close to 500 people worldwide.

As of January 31, 2020, the Canadian government has confirmed four cases of the 2019 novel coronavirus in Canada, three cases in Ontario and one in British Columbia.

Canadians with upcoming travel plans, in the middle of a trip, as well as those who have recently returned from overseas, are advised to become informed on the current outbreak and take the necessary precautions to ensure their safety and that of those around them.

Read more…

Travel Health News – February 2019

A white page appears on a wooden desktop next to two starfish and a passport with money and a ticket inside. It says "Travel Health Alerts FEB 2019 Measles, Polio, and Zika Virus outbreaks in popular destinations. traveldoc.ca"

Measles outbreaks keep spreading to popular travel destinations.

The Centers for Disease Control and Prevention has issued travel notices for the following countries:

Brazil, Colombia, Congo, England, France, Greece Indonesia, Isreal, Italy, Japan, Kazakhstan, Madagascar, Moldova, the Phillippines, Romania, Serbia, and Ukraine.

Travellers are advised to receive the measles-mumps-rubella (MMR) vaccine before leaving the country.

Pregnant women are warned not to travel to India after reports of a Zika virus outbreak.

The Zika virus may cause severe birth defects and is spread through sex and mosquito bites.

Polio outbreak in Indonesia due to low vaccination rates.

The CDC advises adults heading to Indonesia get a single, lifetime Polio booster shot following the Polio vaccinations received during childhood.

Measles Outbreaks Reported in Israel, New Zealand, Moldova, and Colombia [Updated]

The stomach of a child wearing a green shirt, and who is being held up by two adult hands, is shown with a red bumpy measles rash.Travellers planning trips to Israel, New Zealand, Moldova, or Colombia should get vaccinated against the measles before departing, warns the Centers for Disease Control and Prevention (CDC).

On Nov. 16, the CDC released three separate travel alerts after health officials reported outbreaks of the virus in Israel, New Zealand,  and Moldova. Four days later, the health agency also warned travellers about a measles outbreak in Colombia.*

The measles is an infectious airborne disease spread by breathing, coughing, and sneezing, which may result in serious complications leading to pneumonia or death. Signs and symptoms include a rash, high fever, cough, runny nose, as well as red and watery eyes. Read more…

CDC Warns Pregnant Travellers about Rubella Outbreak in Japan

Travellers headed to Japan should get vaccinated against rubella to protect themselves from an outbreak in the country, advises the Centers for Disease Control and Prevention (CDC).

Rubella is an infectious disease spread by sneezes and coughs.  Also referred to as the “German Measles,” it causes rashes and fevers that usually last between two and three days and symptoms are often mild.

Prior to entering Japan, the CDC recommends travellers receive the MMR (measles, mumps, and rubella) vaccine.

Pregnant women, however, are warned not to enter the country due to the risks the rubella virus poses to developing babies. It is known to cause birth defects such as mental disabilities, deafness, cataracts, and organ damage.

Japanese health officials report that most cases are occurring in the Kanto region in locations such as Tokyo, Kanagawa, Chiba, and Saitama.

Source: CDC