Outbreaks 101: Vaccine "Ring Strategy" Explained

August 25, 2020

John Johnson, lead for Ebola vaccination with MSF France, describes the "ring strategy" used in controlling several infectious disease threats.

The World Health Organization (WHO) reported that the emerging Ebola outbreak in western Democratic Republic of Congo (DRC) has infected at least 100 people as of last week. Of these 100 people, at least 43 have passed.

The US Centers for Disease Control and Prevention recently issued a level 2 travel notice for Ebola in DRC based on the situation in Équateur province.

The last outbreak of Ebola, in Kivu, only just ended as the current one in Équateur began. The new Ebola outbreak is in a less volatile region in terms of armed conflict, however there are still substantial challenges ahead.

Of particular note have been demonstrations by local health care workers in Mbandaka, who argue that they are putting their lives on the line despite low pay scales and delays with paychecks.

During the outbreak in Kivu, Contagion spoke with John Johnson, an emergency coordinator at Doctors Without Borders.

In the following clip, Johnson describes the vaccine "ring strategy" used historically in controlling several infectious disease threats, including the recent Ebola outbreak.

WHO has already began using the ring strategy in Équateur, with health workers racing to reach remote rural areas and perform contact tracing.

John Johnson, lead for Ebola vaccination with MSF France, describes the "ring strategy" used in controlling several infectious disease threats.Contagion: What role has vaccination had in this in this response? And why was the additional Johnson and Johnson vaccine brought in? Has it been helpful to have that additional tool in the arsenal, those sorts of things?

Johnson: The rVSV vaccine is really a game changer. We see that it's an effective vaccine. After the West African outbreak this was the vaccine that was the most advanced and the most studied. There was a global stockpile created of about 300,000 doses.

When we started using the Merck vaccine it was 300,000 doses, that's a lot for an Ebola outbreak. Most Ebola outbreaks are less than 100 patients. You wouldn't need a large stockpile. And nobody really expected another large Ebola outbreak anytime soon.

When we started vaccinating right away in August of 2018, things were going fine until we started really worrying about if we would run out of Merck vaccines. It was at this point that people started looking for plan B.

But just to give you a bit of background on the role that vaccines played, the strategy that was used for the deployment of Merck was what they call a ring strategy. The ring strategy is nothing new. It's what was used to eradicate smallpox. To very briefly explain the ring strategy, what you do is you take your index case, you vaccinate their contacts—so anyone that they've come in contact with the past few days—and then you go to those contacts, and you make a list of the people they've been in contact with over the past few days, and you vaccinate their contacts. So it's called the ring strategy because it's a ring around the patient, and then a second ring around the contacts.

The people that have already been exposed to Ebola, may or may not have already developed the virus in their body and we may be vaccinating someone who already has Ebola but hasn't exhibited symptoms. The protection really starts at the second ring, the second line of contacts of contacts. But what we saw with a Merck vaccine was that there was also some protection offered to people even if they'd already been exposed to Ebola. It did reduce the risk of mortality.

We were using the ring strategy with [the Merck vaccine]. But the problem with the ring strategy, well, there's no problem with a ring strategy. Theoretically, it's quite sound. The problem was always with the implementation of it. In the context of North Kivu where there's a mobile population, and people that are already somewhat resistant to the Ebola response, we never were able to vaccinate enough people because we were never able to identify and follow all of the contacts.

The interest in having a second vaccine, for example, the J&J [Johnson and Johnson] vaccine has a global stockpile of 1.5 million doses. And with that vaccine, we could do a complimentary strategy, where contacts and contacts and contacts get the Merck vaccine, which is now proven to be very effective, and the J&J Vaccine could be used for a larger percentage of the population living in those areas that are affected but have not come into direct contact.

That would therefore be a preventive strategy for these populations at risk.

[For the full podcast this clip was taken from, see here.]

Full Podcast Description:

Ebola: Past, Present, Future

"First, we'll speak to John Johnson, project lead for Ebola vaccination in the Democratic Republic of the Congo with Médecins Sans Frontières France, for a perspective on how the new availability of vaccines has shaped the response to the ongoing epidemic compared to the West African Ebola outbreak.

Then, we'll speak with microbiologist Jason Kindrachuk, PhD, about his experience in Liberia during the West African epidemic. Kindrachuk is also an expert on current research pertaining to lasting effects in Ebola survivors, so we'll speak to him for a clinical perspective on what the future holds for those who survive the disease."

A transcript of the interview is available here.