Avoiding COVID-19 infections with effective vaccine programs

COVID-19 VACCINE

Speed and trust

Keys to an effective vaccination program

Highly effective COVID-19 vaccines are now available, but their mere existence is not enough to end a pandemic that has infected more than 110 million people globally and killed about 2.5 million. People will continue to get sick if vaccine rollout is slow, the novel coronavirus is spreading rapidly or people do not trust the vaccines and decline to get a shot.

Supply shortages have hobbled vaccine rollout in many of the world’s richest nations while many poorer countries still have virtually no access to the vaccines. Some countries are still struggling to convince their people that the vaccines are safe and effective, while new variants of the virus are proving to be more transmissible than earlier forms.

A study by researchers at the Yale School of Public Health and Harvard Medical School details how these three elements – pace of rollout, infection rate, and trust in the vaccine – interact and what the stakes are in terms of reducing further COVID-19 infections.

Pace

Infection

Trust

rate

of vaccination

in vaccine

How many infections

can a vaccine help avoid?

Pace

Infection

Trust

of vaccination

rate

in vaccine

How many infections

can a vaccine help avoid?

“Vaccines don’t save lives, vaccination programs save lives,” said David Paltiel, a professor at the Yale School of Public Health who led the study.

To examine how an effective vaccine program can lower case counts, Reuters simulated how a disease resembling COVID-19 might spread through a population over the course of six months, using the model from the study. Here is a look at how each factor of the vaccine rollout affects the number of infections avoided.

Pace

The pace of vaccination – percentage of the population being vaccinated per day – heavily influences how many infections can be avoided. In most cases, when doses are administered more quickly, a lower number of infections follows.

The charts below show the percentage of the population that has received at least one dose of a COVID-19 vaccine, and the pace at which people are being vaccinated, averaged over the past 14 days. This may not equal the percentage of the population that is fully vaccinated if the vaccine requires two doses.

Pace of COVID-19 vaccination

Israel

Chile

United Kingdom

0.74% per day (latest 14 day avg.)

0.51% per day

0.73% per day

50%

25%

Cumulative share of

population vaccinated

0

Jan. 1

Feb. 23

United States

Germany

India

0.25% per day

0.09% per day

0.02% per day

50%

25%

0

Israel

United Kingdom

0.74% per day (latest 14 day avg.)

0.51% per day

50%

25%

Cumulative share of

population vaccinated

0

Jan. 1

Feb. 23

United States

Chile

0.73% per day

0.25% per day

Germany

India

0.09% per day

0.02% per day

The following scenarios assume that each person in a population needs two doses to be fully vaccinated, and that everyone does receive two doses. Most approved COVID-19 vaccines require two doses.

Rate of infection

The scenarios above assume that the virus is spreading moderately, with each infected person spreading it on average to 1.2 others. What happens if people stop practicing social distancing, lockdowns are eased or highly infectious variants appear and the virus spreads more rapidly? Even with a high pace of vaccination, case counts would grow.

“Right now, the virus is behaving like an out-of-control wildfire in our community,” Paltiel said, stressing the importance of keeping the rate of spread low. “If I have a bucket of water, I could put out a campfire. But a bucket of water isn’t going to do any good in putting out a forest fire.”

Public trust

When the virus is spreading quickly, a high pace of vaccination is not enough to curb infections. This is when public trust in the COVID-19 vaccines becomes critical - and such trust varies across the globe and within individual countries. In countries where such trust is low, supply can outstrip demand.

People’s willingness to get the COVID-19 vaccine

Speed and trust are both important

Keeping infection rates down by social distancing and wearing masks can help a vaccination program be more effective. When the virus is spreading fast, pace of vaccination and people’s willingness to be vaccinated both become crucial factors.

High pace, low trust

Low pace, high trust

High pace and trust

While governments have struggled to roll out the COVID-19 vaccine quickly because of logistical and supply challenges, the pace of vaccination could accelerate in some countries.

Global case counts have fallen to their lowest levels since last October, with public health leaders hoping that mass vaccination can keep the trends heading in the right direction.

“Now is not the time to let your guard down,” said Maria Van Kerkhove, the World Health Organization’s technical lead on COVID-19. “We cannot let ourselves get into a situation where we have cases rise again.”

Methodology

The data in all the scenarios presented here is based on a study published in the journal Health Affairs titled “Clinical Outcomes Of A COVID-19 Vaccine: Implementation Over Efficacy” by researchers at the Yale School of Public Health and the Harvard Medical School.

The data assumes that the vaccine is 75% effective, requires two doses, and takes effect after 30 days. The vaccine is assumed to be a disease-modifying one that improves the course of disease in infected people and slows disease progression.

The scenarios presented consider: vaccination pace of 0.1%, 0.5% and 2%; the rate of spread, or the effective reproductive number, of 1.2, 1.8 and 2.1; and coverage, or the percentage of the population willing to get vaccinated, at 25%, 50% and 75%.

Edited by

Jon McClure and Will Dunham