When will the COVID-19 pandemic end?

IMHO and what do I know? I am a scientist and not a doctor.

The pandemic will end when either:

  • The virus stops killing people, and making people seriously ill, or 
  • Population immunity is achieved

The Virus Stops Killing People and Making People Seriously Ill

The virus could mutate to a less deadly and threatening version. However, as the virus mutation rate is low, this is unlikely.

A vaccine could provide sufficient protection to stop people dying from the infection. For example, whilst, the Astra Zeneca vaccine had an efficacy rate of 70% against the original Wuhan strain (preventing you from getting infected), it is to reported to be 100% effective at preventing people being admitted to hospital from the Wuhan strain.

Consideration will also need to be given to preventing large numbers of people getting long COVID.

If all the people who are susceptible to becoming seriously ill (being admitted to hospital or getting long COVID) and those who are susceptible to dying from COVID-19 are effectively vaccinated then the pandemic would effectively be at an end. People would still get infected, but they would no longer end up in hospital, or get long COVID.

Population Immunity is Achieved

If a large enough percentage of people who are susceptible to the virus come in to contact with it, either by being infected with the virus, or by being vaccinated, the virus will die out.

Population immunity or herd immunity, is a concept used for vaccination, in which a population can be protected from a certain virus if a threshold of vaccination is reached. For example, population immunity against measles requires about 95% of a population to be vaccinated. The remaining 5% will be protected by the fact that measles will not spread among those who are vaccinated.

The population immunity for the original Wuhan strain of Covid-19 is estimated at approximately 60%. Population immunity threshold = 1−1/R0 (where R0 is the disease’s basic reproduction number, R0 for Covid-19 estimated to be between 2 and 3).

The Alpha variant of COVID-19, discovered in the UK, is estimated to be 70% more transmissible than the original virus, its R0 could therefore be between 3.5 and 5. If this were the case the herd immunity threshold (HIT) would increase to approximately 75% (1-1/4).

The Delta variant of COVID-19, discovered in India, is estimated by Public Health England to be 60% more transmissible than the Alpha variant, its R0 could therefore be between 5.5 and 8. If this were the case the herd immunity threshold (HIT) would increase to approximately 86% (1-1/7).

Vaccination is Important

To ensure the Pandemic ends quickly whilst minimizing deaths it is important that as many people as possible get vaccinated against the disease as quickly as possible.

When will the Pandemic End?

For the pandemic to end a sufficiently large number of people’ s immune systems most come into contact with the virus. When this will be is currently unknown.

People can either be vaccinated, or catch the virus.

There is not an option of hoping it will go away and doing nothing. You either get the vaccine or you get the virus.

Can the Vaccines Stop the Pandemic?

To achieve the Herd Immunity Threshold (HIT) against the Delta variant of COVID-19 we need 86% of the population to be immune to it. If this threshold is reached cases of the virus should over time disappear completely.

In the real world the following evidence has been reported for the effectiveness of vaccines.

The Pfizer vaccine was found to be 88% effective at stopping symptomatic disease from the Delta(Indian) variant two weeks after the second dose, compared with 93% effectiveness against the Alpha (UK-Kent) variant.

The AstraZeneca jab was 60% effective against the Delta (Indian) variant, compared with 66% against the Alpha (UK-Kent) variant.

It is clear from this that the AstraZeneca vaccine can not stop symptomatic cases of the Delta (Indian) variant of COVID-19, even if the whole population was vaccinated. The effectiveness of the vaccine at 60% is considerably less than the required 86% herd immunity threshold. However, the Astra Zeneca vaccine is 92% effective at stopping people becoming seriously ill and being admitted to hospital.

If the whole population was vaccinated with the Pfizer vaccine this would be sufficient to achieve the Herd Immunity Threshold.

If both Astra Zeneca and Pfizer vaccines are used within a population it will not be possible to achieve Herd Immunity by vaccination alone. A percentage of the population will need to obtain natural immunity via infection with the virus for Herd Immunity to be achieved.

In the UK the AstraZeneca vaccine accounts for 70% of vaccinations administered.

This means that in the UK we would expect the proportion of the vaccinated population to be protected against symptomatic disease caused by the Delta (Indian) variant to be 0.7 x 0.6 + 0.3 x 0.88 = 68.4%

If 50% of UK adults have received 2 doses of the vaccine 0.5 x 0.684 = 34% of the population would be protected as a result of vaccination against symptomatic disease.